Engine start and run quality at various temperatures is typically dependent on fuel enrichment. A proper variation of fuel enrichment for a naturally aspirated gasoline engine can be achieved by way of a carburetor and a choke plate used in conjunction with one another. Generally speaking, the choke plate is capable of operating to constrict the flow of air into the carburetor inlet, such that the air passing through the constricted inlet passes through a smaller opening resulting in an increased velocity and decreased pressure within the body (venturi) of the carburetor downstream of the inlet. Reducing the pressure through the body (venturi) of the carburetor increases the pressure differential at the fuel source, thereby increasing the amount of fuel flowing into and through the venturi section of the carburetor body.
Typically it is desirable to vary the positioning of a choke plate in an engine depending upon engine operational circumstances. In particular, it typically is desirable to have more fuel entering the engine relative to the amount of air entering the engine when the engine is cold and/or first starting, and so it is commonly the case that a choke plate will be positioned so as to block more air flow at the carburetor inlet under these circumstances (moved to its “closed” position), while positioned so as not to block as much air flow or any air flow at other times (moved to its “open” position). To avoid having to manually adjust the position of the choke plate during start-up and at other running conditions of the engine, automatic choking control systems (also referred to as auto-choke systems or automatic choke systems) are often employed.
Although automatic choke systems are widely employed in the automotive industry, cable controlled choke systems are more common in the small engine industry, particularly small engines employed in consumer applications (e.g., engines for use in lawnmowers, snow throwers, snow blowers, etc.), due largely to the complexity and high cost of existing automatic choke systems. Further, the automatic choke systems that do exist for application in the small engine consumer market are nevertheless inadequate in at least some respects. For example, many conventional automatic choke systems for use in small engines are inadequately designed, such that during operation the systems can result in undesirable engine performance including, for example, generation of black smoke during start-up or during warm-up conditions, contamination of engine oil with fuel, and engine spark plug fouling. Also, many conventional automatic choke systems for small engines do not account for variations in engine and carburetor design that necessitate varying degrees of choking during the restarting of an engine, after the engine has been running, during cool-down of the engine, and under other application load conditions.
It would therefore be advantageous if an improved automatic choke system was designed that could serve to properly choke (or avoid choking) the engine carburetor to achieve or enhance one or more desired types of operational behavior of the engine (e.g., quick start-up) under one or more operational circumstances. In at least some embodiments, it would be advantageous if such an improved automatic choke system was capable of manipulating the choke plate in response to engine temperature and/or engine load demand, was capable of fully opening the choke plate once the engine was fully warm (or at a temperature at which choke is not desired), and/or was capable of adjusting choke operation for start-up, warm-up, restart, cool-down, application load conditions, and/or other conditions. In at least some further embodiments, it would be advantageous if such an automatic choke system was simpler and/or less costly than conventional automatic choke systems.